Zebra Mussels (Dreissena polymorpha) are originally from Eastern European seas but have managed to spread around the world in the ballast water of ocean-navigating ships. The first established population in the United States was sighted in 1988 within the waters of Lake St. Clair. Since Lake St. Clair connects to both Lakes Huron and Erie, the spread was rapid. Today Zebra Mussels are found in 29 different states, infesting the Great Lakes region and Mississippi River basin. Photo courtesy of the USGS
Zebra Mussels can cause a multitude of environmental issues for the native plants and animals surrounding them. Zebra Mussels need to attach to a solid surface in order to survive. This surface can be anything they find in the water; manmade objects, plant vegetation, crayfish, turtles, and even the native mussel species. When the Zebra Mussel attaches to a native mussel it will limit mobility, limit access to food supply, and ultimately kill the native mussel. Another major problem with Zebra Mussels is the amount of water a single one can filter through in a day. In a single day, one Zebra Mussel can filter through 1 litre of water. This in turn will make the infested waters much clearer, which allows sunlight to reach deeper and produce hardier plant life. In the end this inhibits recreational activities similar to swimming and boating.
Prevention of Zebra Mussel spread is difficult to maintain but necessary to protect home waters from this rapidly reproducing mussel. According to the Indianapolis DNR: "Over one spawning season a single female zebra mussel is capable of releasing one million eggs." If fertilized, those eggs will turn into microscopic larvae which feed for a few weeks before attaching to their permanent solid surface. Some native fish species do feed on the mussels like yellow perch, sturgeon, and catfish. Unfortunately, the reproduction rate of the Zebra Mussels is rapid enough that the predators only have a small effect.
The best prevention technique is to practice aquatic hygiene. Cleaning plants and animals from your recreational equipment when leaving a water body is important. Also, emptying your bait bucket into a water body has the potential to spread the larvae, so it's best to empty your bucket on land instead. Finally, draining your boat's live wells and washing it in hot water will prevent the dispersal of the species.
This PDF from the Indiana Department of Natural Resources is an excellent fact sheet on Zebra Mussels moving into the country.